This invention relates to a capacitor element for use in a semiconductor integrated circuit and a method of manufacturing the same.
When used in a (semiconductor) integrated circuit, a capacitor is often referred to herein as a capacitor element. In an integrated circuit, a capacitor element is used in carrying out direct-current blocking and/or peaking. The capacitor element is alternatively used to store data in a dynamic random access memory (DRAM) or in a like semiconductor memory device. Such a capacitor element has been a diffused capacitor of a p-n junction, a metal oxide semiconductor (MOS) capacitor, or a metal insulator semiconductor (MIS) capacitor. In any event, it is well known that a capacitor element comprises a pair of opposing capacitor electrodes and a dielectric film or layer between the (capacitor) electrodes.
In the manner which will later be described in greater detail, a metal insulator semiconductor capacitor comprises a highly doped semiconductor layer in a semiconductor substrate as a first conductor layer having a conductor surface opposite to the substrate. An insulator film is formed on the conductor surface as a dielectric film having a dielectric surface. A metal layer is formed on the dielectric surface as a second conductor layer. Alternatively, the first conductor layer may be another metal layer formed on the semiconductor substrate.
The dielectric film has been either a film of an oxide of a semiconductor material, such as silicon, of the semiconductor substrate or a nitride film. The dielectric film consequently has a relatively low dielectric constant. The dielectric film must therefore either have a wide film area or have a very thin film thickness in order to give a desired capacitance to the capacitor element. When the dielectric film has a wide film area, it becomes impossible to manufacture a highly integrated circuit. When the dielectric film has a thin film thickness, the capacitor element becomes unreliable.
Recently, attention has been directed to a tantalum oxide film and a perovskite oxide film. The perovskite oxide is typically strontium titanate (SrTiO.sub.3) or a composite of lead zirconate and lead titanate. The composite is known by the trade name of PZT and will herein be so called merely for brevity of the description.
The tantalum oxide film or the perovskite oxide film has a high dielectric constant and would provide a compact capacitor element. It has, however, been very difficult to prevent a spurious oxide film from undesiredly growing during manufacture of the capacitor element between the dielectric film and each of the first and the second conductor layers. The spurious oxide film objectionably reduces the capacitance and renders the capacitor element unreliable.